Electronic Devices with Low Phase Noise Frequency Generation

ABSTRACT

An electronic device may include clocking circuitry with primary and secondary lasers that generate first and second optical local oscillator (LO) signals. A phase-locked loop (PLL) may tune the secondary laser based to phase lock the first and second optical LO signals. A self-injection locking loop path may couple an output of the secondary laser to its input. The self-injection locking loop path may include a first mixer and a second mixer. The first mixer may generate a beat signal using the first and second optical LO signals. The second mixer may generate a self-injection locking signal based on the first optical LO signal and the beat signal. A delay line or optical resonator may iteratively self-inject the self-injection locking signal onto the secondary laser. This may serve to minimize phase noise and jitter of the optical LO signals.

This application claims the benefit of U.S. Provisional PatentApplication No. 63/335,608, filed Apr. 27, 2022, which is herebyincorporated by reference herein in its entirety.

FIELD

This disclosure relates generally to electronic devices and, moreparticularly, to electronic devices with wireless circuitry.

BACKGROUND

Electronic devices are often provided with wireless capabilities. Anelectronic device with wireless capabilities has wireless circuitry thatincludes one or more antennas. The wireless circuitry is used to performcommunications using radio-frequency signals conveyed by the antennas.

As software applications on electronic devices become moredata-intensive over time, demand has grown for electronic devices thatsupport wireless communications at higher data rates. However, themaximum data rate supported by electronic devices is limited by thefrequency of the radio-frequency signals. As communication frequenciesincrease, it can become difficult to provide low jitter and low phasenoise clocking for the wireless circuitry.

SUMMARY

An electronic device may include wireless circuitry that conveyswireless signals at frequencies greater than 100 GHz. The wirelesscircuitry or other circuitry in the device may be clocked using clockingcircuitry. The clocking circuitry may include a primary laser that emitsa first optical local oscillator (LO) signal at a fixed first frequencyand a secondary laser that emits a second optical LO signal at anadjustable second frequency. The wireless circuitry may, for example,convey the wireless signals using the first and second optical LOsignals.

A phase-locked loop (PLL) path may couple an output of the secondarylaser to an input of the secondary laser. A photodiode may be interposedon the PLL path. The photodiode may generate a photodiode signal basedon the first and second optical LO signals. The clocking circuitry mayinclude a reference oscillator that generates a reference oscillatorsignal. The PLL path may tune the secondary laser based on the referenceoscillator signal and the photodiode signal to phase lock the secondoptical LO signal to the first optical LO signal.

A self-injection locking loop path may also couple an output of thesecondary laser to an input of the secondary laser. The self-injectionlocking loop path may include a first mixer such as a photodiode and asecond mixer such as an electro-optical modulator. The first mixer maygenerate a beat signal using the first and second optical LO signals.The second mixer may generate a self-injection locking signal based onthe first optical LO signal and the beat signal. A delay line or anoptical resonator coupled between the second mixer and the secondarylaser may de-correlate phase noise of the secondary laser by filteringthe self-injection locking signal and self-injecting the self-injectionlocking signal into the secondary laser. Alternatively, the delay lineor optical resonator may be coupled between the output of the firstmixer and the input of the second mixer. This process may iterate untilphase noise of the secondary laser is sufficiently reduced. This mayserve to minimize phase noise and jitter of the optical LO signals whilealso minimizing power consumption and chip area.

An aspect of the disclosure provides clocking circuitry. The clockingcircuitry can include a first light source configured to generate afirst optical LO signal at a first frequency. The clocking circuitry caninclude a second light source configured to generate a second optical LOsignal at a second frequency different from the first frequency. Theclocking circuitry can include a first mixer having a first inputoptically coupled to the first light source and having a second inputoptically coupled to the second light source. The clocking circuitry caninclude a second mixer having a first input optically coupled to thefirst light source, a second input communicably coupled to an output ofthe first mixer, and an output communicably coupled to the second lightsource.

An aspect of the disclosure provides clocking circuitry. The clockingcircuitry can include a first laser configured to generate a firstoptical local oscillator (LO) signal. The clocking circuitry can includea second laser configured to generate a second optical LO signal. Theclocking circuitry can include a phase-locked loop (PLL) path coupledaround the second laser and configured to lock a phase of the secondoptical LO signal to a phase of the first optical LO signal. Theclocking circuitry can include a self-injection locking loop pathcoupled around the second laser and configured to reduce a phase noiseof the second optical LO signal by self-injecting the second laser.

An aspect of the disclosure provides a method of operating wirelesscircuitry to transmit wireless signals. The method can include emitting,at a first laser, a first optical local oscillator (LO) signal at afirst frequency. The method can include emitting, at a second laser, asecond optical LO signal at a second frequency that is different fromthe first frequency. The method can include producing, at a firstphotodiode illuminated by the first optical LO signal and the secondoptical LO signal, an antenna current on an antenna resonating element,the antenna current having a third frequency given by a differencebetween the first frequency and the second frequency. The method caninclude generating, at a second photodiode, a beat signal based on thefirst optical LO signal and the second optical LO signal, the beatsignal having the third frequency. The method can include generating, ata mixer, a self-injection locking signal based on the beat signal andthe first optical LO signal. The method can include self-injectionlocking the second laser based on the self-injection locking signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an illustrative electronic device havingwireless circuitry with at least one antenna that conveys wirelesssignals at frequencies greater than about 100 GHz in accordance withsome embodiments.

FIG. 2 is a top view of an illustrative antenna that transmits wirelesssignals at frequencies greater than about 100 GHz based on optical localoscillator (LO) signals in accordance with some embodiments.

FIG. 3 is a top view showing how an illustrative antenna of the typeshown in FIG. 2 may convert received wireless signals at frequenciesgreater than about 100 GHz into intermediate frequency signals based onoptical LO signals in accordance with some embodiments.

FIG. 4 is a top view showing how multiple antennas of the type shown inFIGS. 2 and 3 may be stacked to cover multiple polarizations inaccordance with some embodiments.

FIG. 5 is a top view showing how stacked antennas of the type shown inFIG. 4 may be integrated into a phased antenna array for conveyingwireless signals at frequencies greater than about 100 GHz within acorresponding signal beam.

FIG. 6 is a circuit diagram of illustrative wireless circuitry having anantenna that transmits wireless signals at frequencies greater thanabout 100 GHz and that receives wireless signals at frequencies greaterthan about 100 GHz for conversion to intermediate frequencies and thento the optical domain in accordance with some embodiments.

FIG. 7 is a circuit diagram of an illustrative phased antenna array thatconveys wireless signals at frequencies greater than about 100 GHzwithin a corresponding signal beam in accordance with some embodiments.

FIG. 8 is a circuit diagram of illustrative clocking circuitry havingprimary and secondary light sources, a self-injection locking loop, anda phase-locked loop that are used to emit low jitter and low phase noiseoptical local oscillator signals in accordance with some embodiments.

FIG. 9 is a circuit diagram of illustrative self-injection lockingcircuitry that includes a delay line that operates on a beat signal inaccordance with some embodiments.

FIG. 10 is a circuit diagram of illustrative self-injection lockingcircuitry that includes a resonator that performs self-injection lockingon a secondary light source in accordance with some embodiments.

FIG. 11 is a flow chart of illustrative operations involved in usingclocking circuitry to emit low jitter and low phase noise optical localoscillator signals using at least a phase-locked loop and self-injectionlocking in accordance with some embodiments.

FIG. 12 is a flow chart of illustrative operations involved in using aphase-locked loop in clocking circuitry to coarsely tune a secondarylight source in accordance with some embodiments.

FIG. 13 is a flow chart of illustrative operations involved in usingself-injection locking circuitry in clocking circuitry to finely tune asecondary light source in accordance with some embodiments.

DETAILED DESCRIPTION

Electronic device 10 of FIG. 1 (sometimes referred to herein aselectro-optical device 10) may be a computing device such as a laptopcomputer, a desktop computer, a computer monitor containing an embeddedcomputer, a tablet computer, a cellular telephone, a media player, orother handheld or portable electronic device, a smaller device such as awristwatch device, a pendant device, a headphone or earpiece device, adevice embedded in eyeglasses, goggles, or other equipment worn on auser's head, or other wearable or miniature device, a television, acomputer display that does not contain an embedded computer, a gamingdevice, a navigation device, an embedded system such as a system inwhich electronic equipment with a display is mounted in a kiosk orautomobile, a wireless internet-connected voice-controlled speaker, ahome entertainment device, a remote control device, a gaming controller,a peripheral user input device, a wireless base station or access point,equipment that implements the functionality of two or more of thesedevices, or other electronic equipment.

As shown in the functional block diagram of FIG. 1 , device 10 mayinclude components located on or within an electronic device housingsuch as housing 12. Housing 12, which may sometimes be referred to as acase, may be formed of plastic, glass, ceramics, fiber composites, metal(e.g., stainless steel, aluminum, metal alloys, etc.), other suitablematerials, or a combination of these materials. In some situations,parts or all of housing 12 may be formed from dielectric or otherlow-conductivity material (e.g., glass, ceramic, plastic, sapphire,etc.). In other situations, housing 12 or at least some of thestructures that make up housing 12 may be formed from metal elements.

Device 10 may include control circuitry 14. Control circuitry 14 mayinclude storage such as storage circuitry 16. Storage circuitry 16 mayinclude hard disk drive storage, nonvolatile memory (e.g., flash memoryor other electrically-programmable-read-only memory configured to form asolid-state drive), volatile memory (e.g., static or dynamicrandom-access-memory), etc. Storage circuitry 16 may include storagethat is integrated within device 10 and/or removable storage media.

Control circuitry 14 may include processing circuitry such as processingcircuitry 18. Processing circuitry 18 may be used to control theoperation of device 10. Processing circuitry 18 may include one or moreprocessors, microprocessors, microcontrollers, digital signalprocessors, host processors, baseband processor integrated circuits,application specific integrated circuits, central processing units(CPUs), graphics processing units (GPUs), etc. Control circuitry 14 maybe configured to perform operations in device 10 using hardware (e.g.,dedicated hardware or circuitry), firmware, and/or software. Softwarecode for performing operations in device 10 may be stored on storagecircuitry 16 (e.g., storage circuitry 16 may include non-transitory(tangible) computer readable storage media that stores the softwarecode). The software code may sometimes be referred to as programinstructions, software, data, instructions, or code. Software codestored on storage circuitry 16 may be executed by processing circuitry18.

Control circuitry 14 may be used to run software on device 10 such assatellite navigation applications, internet browsing applications,voice-over-internet-protocol (VOIP) telephone call applications, emailapplications, media playback applications, operating system functions,etc. To support interactions with external equipment, control circuitry14 may be used in implementing communications protocols. Communicationsprotocols that may be implemented using control circuitry 14 includeinternet protocols, wireless local area network (WLAN) protocols (e.g.,IEEE 802.11 protocols—sometimes referred to as Wi-Fi®), protocols forother short-range wireless communications links such as the Bluetooth®protocol or other wireless personal area network (WPAN) protocols, IEEE802.11ad protocols (e.g., ultra-wideband protocols), cellular telephoneprotocols (e.g., 3G protocols, 4G (LTE) protocols, 3GPP Fifth Generation(5G) New Radio (NR) protocols, Sixth Generation (6G) protocols, sub-THzprotocols, THz protocols, etc.), antenna diversity protocols, satellitenavigation system protocols (e.g., global positioning system (GPS)protocols, global navigation satellite system (GLONASS) protocols,etc.), antenna-based spatial ranging protocols, optical communicationsprotocols, or any other desired communications protocols. Eachcommunications protocol may be associated with a corresponding radioaccess technology (RAT) that specifies the physical connectionmethodology used in implementing the protocol.

Device 10 may include input-output circuitry 20. Input-output circuitry20 may include input-output devices 22. Input-output devices 22 may beused to allow data to be supplied to device 10 and to allow data to beprovided from device 10 to external devices. Input-output devices 22 mayinclude user interface devices, data port devices, and otherinput-output components. For example, input-output devices 22 mayinclude touch sensors, displays (e.g., touch-sensitive and/orforce-sensitive displays), light-emitting components such as displayswithout touch sensor capabilities, buttons (mechanical, capacitive,optical, etc.), scrolling wheels, touch pads, key pads, keyboards,microphones, cameras, buttons, speakers, status indicators, audio jacksand other audio port components, digital data port devices, motionsensors (accelerometers, gyroscopes, and/or compasses that detectmotion), capacitance sensors, proximity sensors, magnetic sensors, forcesensors (e.g., force sensors coupled to a display to detect pressureapplied to the display), temperature sensors, etc. In someconfigurations, keyboards, headphones, displays, pointing devices suchas trackpads, mice, and joysticks, and other input-output devices may becoupled to device 10 using wired or wireless connections (e.g., some ofinput-output devices 22 may be peripherals that are coupled to a mainprocessing unit or other portion of device 10 via a wired or wirelesslink).

Input-output circuitry 20 may include wireless circuitry 24 to supportwireless communications. Wireless circuitry 24 (sometimes referred toherein as wireless communications circuitry 24) may include one or moreantennas 30.

Wireless circuitry 24 may also include transceiver circuitry 26.Transceiver circuitry 26 may include transmitter circuitry, receivercircuitry, modulator circuitry, demodulator circuitry (e.g., one or moremodems), radio-frequency circuitry, one or more radios, intermediatefrequency circuitry, optical transmitter circuitry, optical receivercircuitry, optical light sources, other optical components, basebandcircuitry (e.g., one or more baseband processors), amplifier circuitry,clocking circuitry such as one or more local oscillators and/orphase-locked loops, memory, one or more registers, filter circuitry,switching circuitry, analog-to-digital converter (ADC) circuitry,digital-to-analog converter (DAC) circuitry, radio-frequencytransmission lines, optical fibers, and/or any other circuitry fortransmitting and/or receiving wireless signals using antennas 30. Thecomponents of transceiver circuitry 26 may be implemented on oneintegrated circuit, chip, system-on-chip (SOC), die, printed circuitboard, substrate, or package, or the components of transceiver circuitry26 may be distributed across two or more integrated circuits, chips,SOCs, printed circuit boards, substrates, and/or packages.

The example of FIG. 1 is merely illustrative. While control circuitry 14is shown separately from wireless circuitry 24 in the example of FIG. 1for the sake of clarity, wireless circuitry 24 may include processingcircuitry (e.g., one or more processors) that forms a part of processingcircuitry 18 and/or storage circuitry that forms a part of storagecircuitry 16 of control circuitry 14 (e.g., portions of controlcircuitry 14 may be implemented on wireless circuitry 24). As anexample, control circuitry 14 may include baseband circuitry (e.g., oneor more baseband processors), digital control circuitry, analog controlcircuitry, and/or other control circuitry that forms part of wirelesscircuitry 24. The baseband circuitry may, for example, access acommunication protocol stack on control circuitry 14 (e.g., storagecircuitry 16) to: perform user plane functions at a PHY layer, MAClayer, RLC layer, PDCP layer, SDAP layer, and/or PDU layer, and/or toperform control plane functions at the PHY layer, MAC layer, RLC layer,PDCP layer, RRC, layer, and/or non-access stratum layer.

Transceiver circuitry 26 may be coupled to each antenna 30 in wirelesscircuitry 24 over a respective signal path 28. Each signal path 28 mayinclude one or more radio-frequency transmission lines, waveguides,optical fibers, and/or any other desired lines/paths for conveyingwireless signals between transceiver circuitry 26 and antenna 30.Antennas 30 may be formed using any desired antenna structures forconveying wireless signals. For example, antennas 30 may includeantennas with resonating elements that are formed from dipole antennastructures, planar dipole antenna structures (e.g., bowtie antennastructures), slot antenna structures, loop antenna structures, patchantenna structures, inverted-F antenna structures, planar inverted-Fantenna structures, helical antenna structures, monopole antennas,dipoles, hybrids of these designs, etc. Filter circuitry, switchingcircuitry, impedance matching circuitry, and/or other antenna tuningcomponents may be adjusted to adjust the frequency response and wirelessperformance of antennas 30 over time.

If desired, two or more of antennas 30 may be integrated into a phasedantenna array (sometimes referred to herein as a phased array antenna)in which each of the antennas conveys wireless signals with a respectivephase and magnitude that is adjusted over time so the wireless signalsconstructively and destructively interfere to produce (form) a signalbeam in a given pointing direction. The term “convey wireless signals”as used herein means the transmission and/or reception of the wirelesssignals (e.g., for performing unidirectional and/or bidirectionalwireless communications with external wireless communicationsequipment). Antennas 30 may transmit the wireless signals by radiatingthe signals into free space (or to free space through intervening devicestructures such as a dielectric cover layer). Antennas 30 mayadditionally or alternatively receive the wireless signals from freespace (e.g., through intervening devices structures such as a dielectriccover layer). The transmission and reception of wireless signals byantennas 30 each involve the excitation or resonance of antenna currentson an antenna resonating (radiating) element in the antenna by thewireless signals within the frequency band(s) of operation of theantenna.

Transceiver circuitry 26 may use antenna(s) 30 to transmit and/orreceive wireless signals that convey wireless communications databetween device 10 and external wireless communications equipment (e.g.,one or more other devices such as device 10, a wireless access point orbase station, etc.). The wireless communications data may be conveyedbidirectionally or unidirectionally. The wireless communications datamay, for example, include data that has been encoded into correspondingdata packets such as wireless data associated with a telephone call,streaming media content, internet browsing, wireless data associatedwith software applications running on device 10, email messages, etc.

Additionally or alternatively, wireless circuitry 24 may use antenna(s)30 to perform wireless sensing operations. The sensing operations mayallow device 10 to detect (e.g., sense or identify) the presence,location, orientation, and/or velocity (motion) of objects external todevice 10. Control circuitry 14 may use the detected presence, location,orientation, and/or velocity of the external objects to perform anydesired device operations. As examples, control circuitry 14 may use thedetected presence, location, orientation, and/or velocity of theexternal objects to identify a corresponding user input for one or moresoftware applications running on device 10 such as a gesture inputperformed by the user's hand(s) or other body parts or performed by anexternal stylus, gaming controller, head-mounted device, or otherperipheral devices or accessories, to determine when one or moreantennas 30 needs to be disabled or provided with a reduced maximumtransmit power level (e.g., for satisfying regulatory limits onradio-frequency exposure), to determine how to steer (form) aradio-frequency signal beam produced by antennas 30 for wirelesscircuitry 24 (e.g., in scenarios where antennas 30 include a phasedarray of antennas 30), to map or model the environment around device 10(e.g., to produce a software model of the room where device 10 islocated for use by an augmented reality application, gaming application,map application, home design application, engineering application,etc.), to detect the presence of obstacles in the vicinity of (e.g.,around) device 10 or in the direction of motion of the user of device10, etc.

Wireless circuitry 24 may transmit and/or receive wireless signalswithin corresponding frequency bands of the electromagnetic spectrum(sometimes referred to herein as communications bands or simply as“bands”). The frequency bands handled by communications circuitry 26 mayinclude wireless local area network (WLAN) frequency bands (e.g., Wi-Fi®(IEEE 802.11) or other WLAN communications bands) such as a 2.4 GHz WLANband (e.g., from 2400 to 2480 MHz), a 5 GHz WLAN band (e.g., from 5180to 5825 MHz), a Wi-Fi® 6E band (e.g., from 5925-7125 MHz), and/or otherWi-Fi® bands (e.g., from 1875-5160 MHz), wireless personal area network(WPAN) frequency bands such as the 2.4 GHz Bluetooth® band or other WPANcommunications bands, cellular telephone frequency bands (e.g., bandsfrom about 600 MHz to about 5 GHz, 3G bands, 4G LTE bands, 5G New RadioFrequency Range 1 (FR1) bands below 10 GHz, 5G New Radio Frequency Range2 (FR2) bands between 20 and 60 GHz, etc.), other centimeter ormillimeter wave frequency bands between 10-100 GHz, near-fieldcommunications frequency bands (e.g., at 13.56 MHz), satellitenavigation frequency bands (e.g., a GPS band from 1565 to 1610 MHz, aGlobal Navigation Satellite System (GLONASS) band, a BeiDou NavigationSatellite System (BDS) band, etc.), ultra-wideband (UWB) frequency bandsthat operate under the IEEE 802.15.4 protocol and/or otherultra-wideband communications protocols, communications bands under thefamily of 3GPP wireless communications standards, communications bandsunder the IEEE 802.XX family of standards, and/or any other desiredfrequency bands of interest.

Over time, software applications on electronic devices such as device 10have become more and more data intensive. Wireless circuitry on theelectronic devices therefore needs to support data transfer at higherand higher data rates. In general, the data rates supported by thewireless circuitry are proportional to the frequency of the wirelesssignals conveyed by the wireless circuitry (e.g., higher frequencies cansupport higher data rates than lower frequencies). Wireless circuitry 24may convey centimeter and millimeter wave signals to support relativelyhigh data rates (e.g., because centimeter and millimeter wave signalsare at relatively high frequencies between around 10 GHz and 100 GHz).However, the data rates supported by centimeter and millimeter wavesignals may still be insufficient to meet all the data transfer needs ofdevice 10. To support even higher data rates such as data rates up to5-10 Gbps or higher, wireless circuitry 24 may convey wireless signalsat frequencies greater than 100 GHz.

As shown in FIG. 1 , wireless circuitry 24 may transmit wireless signals32 and may receive wireless signals 34 at frequencies greater thanaround 100 GHz. Wireless signals 32 and 34 may sometimes be referred toherein as tremendously high frequency (THF) signals 32 and 34, sub-THzsignals 32 and 34, THz signals 32 and 34, or sub-millimeter wave signals32 and 34. THF signals 32 and 34 may be at sub-THz or THz frequenciessuch as frequencies between 100 GHz and 1 THz, between 100 GHz and 10THz, between 100 GHz and 2 THz, between 200 GHz and 1 THz, between 300GHz and 1 THz, between 300 GHz and 2 THz, between 300 GHz and 10 THz,between 100 GHz and 800 GHz, between 200 GHz and 1.5 THz, etc. (e.g.,within a sub-THz, THz, THF, or sub-millimeter frequency band such as a6G frequency band). The high data rates supported by these frequenciesmay be leveraged by device 10 to perform cellular telephone voice and/ordata communications (e.g., while supporting spatial multiplexing toprovide further data bandwidth), to perform spatial ranging operationssuch as radar operations to detect the presence, location, and/orvelocity of objects external to device 10, to perform automotive sensing(e.g., with enhanced security), to perform health/body monitoring on auser of device 10 or another person, to perform gas or chemicaldetection, to form a high data rate wireless connection between device10 and another device or peripheral device (e.g., to form a high datarate connection between a display driver on device 10 and a display thatdisplays ultra-high resolution video), to form a remote radio head(e.g., a flexible high data rate connection), to form a THF chip-to-chipconnection within device 10 that supports high data rates (e.g., whereone antenna 30 on a first chip in device 10 transmits THF signals 32 toanother antenna 30 on a second chip in device 10), and/or to perform anyother desired high data rate operations.

Space is at a premium within electronic devices such as device 10. Insome scenarios, different antennas 30 are used to transmit THF signals32 than are used to receive THF signals 34. However, handlingtransmission of THF signals 32 and reception of THF signals 34 usingdifferent antennas 30 can consume an excessive amount of space and otherresources within device 10 because two antennas 30 and signal paths 28would be required to handle both transmission and reception. To minimizespace and resource consumption within device 10, the same antenna 30 andsignal path 28 may be used to both transmit THF signals 32 and toreceive THF signals 34. If desired, multiple antennas 30 in wirelesscircuitry 24 may transmit THF signals 32 and may receive THF signals 34.The antennas may be integrated into a phased antenna array thattransmits THF signals 32 and that receives THF signals 34 within acorresponding signal beam oriented in a selected beam pointingdirection.

It can be challenging to incorporate components into wireless circuitry24 that support wireless communications at these high frequencies. Ifdesired, transceiver circuitry 26 and signal paths 28 may includeoptical components that convey optical signals to support thetransmission of THF signals 32 and the reception of THF signals 34 in aspace and resource-efficient manner. The optical signals may be used intransmitting THF signals 32 at THF frequencies and in receiving THFsignals 34 at THF frequencies.

FIG. 2 is a diagram of an illustrative antenna 30 that may be used toboth transmit THF signals 32 and to receive THF signals 34 using opticalsignals. Antenna 30 may include one or more antenna radiating(resonating) elements such as radiating (resonating) element arms 36. Inthe example of FIG. 2 , antenna 30 is a planar dipole antenna (sometimesreferred to as a “bowtie” antenna) having two opposing radiating elementarms 36 (e.g., bowtie arms or dipole arms). This is merely illustrativeand, in general, antenna 30 may be any type of antenna having anydesired antenna radiating element architecture.

As shown in FIG. 2 , antenna 30 includes a photodiode (PD) 42 coupledbetween radiating element arms 36. Electronic devices that includeantennas 30 with photodiodes 42 such as device 10 may sometimes also bereferred to as electro-optical devices (e.g., electro-optical device10). Photodiode 42 may be a programmable photodiode. An example in whichphotodiode 42 is a programmable uni-travelling-carrier photodiode (UTCPD) is described herein as an example. Photodiode 42 may thereforesometimes be referred to herein as UTC PD 42 or programmable UTC PD 42.This is merely illustrative and, in general, photodiode 42 may includeany desired type of adjustable/programmable photodiode or component thatconverts electromagnetic energy (e.g., light or light energy) at opticalfrequencies (e.g., infrared, visible, and/or ultraviolet frequencies) tocurrent at THF frequencies on radiating element arms 36 and/or viceversa. Each radiating element arm 36 may, for example, have a first edgeat UTC PD 42 and a second edge opposite the first edge that is widerthan the first edge (e.g., in implementations where antenna 30 is abowtie antenna). Other radiating elements may be used if desired.

UTC PD 42 may have a bias terminal 38 that receives one or more controlsignals V_(BIAS). Control signals V_(BIAS) may include bias voltagesprovided at one or more voltage levels and/or other control signals forcontrolling the operation of UTC PD 42 such as impedance adjustmentcontrol signals for adjusting the output impedance of UTC PD 42. Controlcircuitry 14 (FIG. 1 ) may provide (e.g., apply, supply, assert, etc.)control signals V_(BIAS) at different settings (e.g., values,magnitudes, etc.) to dynamically control (e.g., program or adjust) theoperation of UTC PD 42 over time. For example, control signals V_(BIAS)may be used to control whether antenna 30 transmits THF signals 32 orreceives THF signals 34. When control signals V_(BIAS) include a biasvoltage asserted at a first level or magnitude, antenna 30 may beconfigured to transmit THF signals 32. When control signals V_(BIAS)include a bias voltage asserted at a second level or magnitude, antenna30 may be configured to receive THF signals 34. In the example of FIG. 2, control signals V_(BIAS) include the bias voltage asserted at thefirst level to configure antenna 30 to transmit THF signals 32. Ifdesired, control signals V_(BIAS) may also be adjusted to control thewaveform of the THF signals (e.g., as a squaring function that preservesthe modulation of incident optical signals, a linear function, etc.), toperform gain control on the signals conveyed by antenna 30, and/or toadjust the output impedance of UTC PD 42.

As shown in FIG. 2 , UTC PD 42 may be optically coupled to optical path40. Optical path 40 may include one or more optical fibers orwaveguides. UTC PD 42 may receive optical signals from transceivercircuitry 26 (FIG. 1 ) over optical path 40. The optical signals mayinclude a first optical local oscillator (LO) signal LO1 and a secondoptical local oscillator signal LO2. Optical local oscillator signalsLO1 and LO2 may be generated by light sources in transceiver circuitry26 (FIG. 1 ). Optical local oscillator signals LO1 and LO2 may be atoptical wavelengths (e.g., between 400 nm and 700 nm), ultra-violetwavelengths (e.g., near-ultra-violet or extreme ultravioletwavelengths), and/or infrared wavelengths (e.g., near-infraredwavelengths, mid-infrared wavelengths, or far-infrared wavelengths).Optical local oscillator signal LO2 may be offset in wavelength fromoptical local oscillator signal LO1 by a wavelength offset X. Wavelengthoffset X may be equal to the wavelength of the THF signals conveyed byantenna 30 (e.g., between 100 GHz and 1 THz (1000 GHz), between 100 GHzand 2 THz, between 300 GHz and 800 GHz, between 300 GHz and 1 THz,between 300 and 400 GHz, etc.).

During signal transmission, wireless data (e.g., wireless data packets,symbols, frames, etc.) may be modulated onto optical local oscillatorsignal LO2 to produce modulated optical local oscillator signal LO2′. Ifdesired, optical local oscillator signal LO1 may be provided with anoptical phase shift S. Optical path 40 may illuminate UTC PD 42 withoptical local oscillator signal LO1 (plus the optical phase shift S whenapplied) and modulated optical local oscillator signal LO2′. If desired,lenses or other optical components may be interposed between opticalpath 40 and UTC PD 42 to help focus the optical local oscillator signalsonto UTC PD 42.

UTC PD 42 may convert optical local oscillator signal LO1 and modulatedlocal oscillator signal LO2′ (e.g., beats between the two optical localoscillator signals) into antenna currents that run along the perimeterof radiating element arms 36. The frequency of the antenna currents isequal to the frequency difference between local oscillator signal LO1and modulated local oscillator signal LO2′. The antenna currents mayradiate (transmit) THF signals 32 into free space. Control signalV_(BIAS) may control UTC PD 42 to convert the optical local oscillatorsignals into antenna currents on radiating element arms 36 whilepreserving the modulation and thus the wireless data on modulated localoscillator signal LO2′ (e.g., by applying a squaring function to thesignals). THF signals 32 will thereby carry the modulated wireless datafor reception and demodulation by external wireless communicationsequipment.

FIG. 3 is a diagram showing how antenna 30 may receive THF signals 34(e.g., after changing the setting of control signals V_(BIAS) into areception state from the transmission state of FIG. 2 ). As shown inFIG. 3 , THF signals 34 may be incident upon antenna radiating elementarms 36. The incident THF signals 34 may produce antenna currents thatflow around the perimeter of radiating element arms 36. UTC PD 42 mayuse optical local oscillator signal LO1 (plus the optical phase shift Swhen applied), optical local oscillator signal LO2 (e.g., withoutmodulation), and control signals V_(BIAS) (e.g., a bias voltage assertedat the second level) to convert the received THF signals 34 intointermediate frequency signals SIGIF that are output onto intermediatefrequency signal path 44.

The frequency of intermediate frequency signals SIGIF may be equal tothe frequency of THF signals 34 minus the difference between thefrequency of optical local oscillator signal LO1 and the frequency ofoptical local oscillator signal LO2. As an example, intermediatefrequency signals SIGIF may be at lower frequencies than THF signals 32and 34 such as centimeter or millimeter wave frequencies between 10 GHzand 100 GHz, between 30 GHz and 80 GHz, around 60 GHz, etc. If desired,transceiver circuitry 26 (FIG. 1 ) may change the frequency of opticallocal oscillator signal LO1 and/or optical local oscillator signal LO2when switching from transmission to reception or vice versa. UTC PD 42may preserve the data modulation of THF signals 34 in intermediatesignals SIGIF. A receiver in transceiver circuitry 26 (FIG. 1 ) maydemodulate intermediate frequency signals SIGIF (e.g., after furtherdownconversion) to recover the wireless data from THF signals 34. Inanother example, wireless circuitry 24 may convert intermediatefrequency signals SIGIF to the optical domain before recovering thewireless data. In yet another example, intermediate frequency signalpath 44 may be omitted and UTC PD 42 may convert THF signals 34 into theoptical domain for subsequent demodulation and data recovery (e.g., in asideband of the optical signal).

The antenna 30 of FIGS. 2 and 3 may support transmission of THF signals32 and reception of THF signals 34 with a given polarization (e.g., alinear polarization such as a vertical polarization). If desired,wireless circuitry 24 (FIG. 1 ) may include multiple antennas 30 forcovering different polarizations. FIG. 4 is a diagram showing oneexample of how wireless circuitry 24 may include multiple antennas 30for covering different polarizations.

As shown in FIG. 4 , the wireless circuitry may include a first antenna30 such as antenna 30V for covering a first polarization (e.g., a firstlinear polarization such as a vertical polarization) and may include asecond antenna 30 such as antenna 30H for covering a second polarizationdifferent from or orthogonal to the first polarization (e.g., a secondlinear polarization such as a horizontal polarization). Antenna 30V mayhave a UTC PD 42 such as UTC PD 42V coupled between a corresponding pairof radiating element arms 36. Antenna 30H may have a UTC PD 42 such asUTC PD 42H coupled between a corresponding pair of radiating elementarms 36 oriented non-parallel (e.g., orthogonal) to the radiatingelement arms 36 in antenna 30V. This may allow antennas 30V and 30H totransmit THF signals 32 with respective (orthogonal) polarizations andmay allow antennas 30V and 30H to receive THF signals 32 with respective(orthogonal) polarizations.

To minimize space within device 10, antenna 30V may be verticallystacked over or under antenna 30H (e.g., where UTC PD 42V partially orcompletely overlaps UTC PD 42H). In this example, antennas 30V and 30Hmay both be formed on the same substrate such as a rigid or flexibleprinted circuit board. The substrate may include multiple stackeddielectric layers (e.g., layers of ceramic, epoxy, flexible printedcircuit board material, rigid printed circuit board material, etc.). Theradiating element arms 36 in antenna 30V may be formed on a separatelayer of the substrate than the radiating element arms 36 in antenna 30Hor the radiating element arms 36 in antenna 30V may be formed on thesame layer of the substrate as the radiating element arms 36 in antenna30H. UTC PD 42V may be formed on the same layer of the substrate as UTCPD 42H or UTC PD 42V may be formed on a separate layer of the substratethan UTC PD 42H. UTC PD 42V may be formed on the same layer of thesubstrate as the radiating element arms 36 in antenna 30V or may beformed on a separate layer of the substrate as the radiating elementarms 36 in antenna 30V. UTC PD 42H may be formed on the same layer ofthe substrate as the radiating element arms 36 in antenna 30H or may beformed on a separate layer of the substrate as the radiating elementarms 36 in antenna 30H.

If desired, antennas 30 or antennas 30H and 30V of FIG. 4 may beintegrated within a phased antenna array. FIG. 5 is a diagram showingone example of how antennas 30H and 30V may be integrated within aphased antenna array. As shown in FIG. 5 , device 10 may include aphased antenna array 46 of stacked antennas 30H and 30V arranged in arectangular grid of rows and columns. Each of the antennas in phasedantenna array 46 may be formed on the same substrate. This is merelyillustrative. In general, phased antenna array 46 (sometimes referred toas a phased array antenna) may include any desired number of antennas30V and 30H (or non-stacked antennas 30) arranged in any desiredpattern. Each of the antennas in phased antenna array 46 may be providedwith a respective optical phase shift S (FIGS. 2 and 3 ) that configuresthe antennas to collectively transmit THF signals 32 and/or receive THFsignals 34 that sum to form a signal beam of THF signals in a desiredbeam pointing direction. The beam pointing direction may be selected topoint the signal beam towards external communications equipment, towardsa desired external object, away from an external object, etc.

Phased antenna array 46 may occupy relatively little space within device10. For example, each antenna 30V/30H may have a length 48 (e.g., asmeasured from the end of one radiating element arm to the opposing endof the opposite radiating element arm). Length 48 may be approximatelyequal to one-half the wavelength of THF signals 32 and 34. For example,length 48 may be as small as 0.5 mm or less. Each UTC-PD 42 in phasedantenna array 46 may occupy a lateral area of 100 square microns orless. This may allow phased antenna array 46 to occupy very little areawithin device 10, thereby allowing the phased antenna array to beintegrated within different portions of device 10 while still allowingother space for device components. The examples of FIGS. 2-5 are merelyillustrative and, in general, each antenna may have any desired antennaradiating element architecture.

FIG. 6 is a circuit diagram showing how a given antenna 30 and signalpath 28 (FIG. 1 ) may be used to both transmit THF signals 32 andreceive THF signals 34 based on optical local oscillator signals. In theexample of FIG. 6 , UTC PD 42 converts received THF signals 34 intointermediate frequency signals SIGIF that are then converted to theoptical domain for recovering the wireless data from the received THFsignals.

As shown in FIG. 6 , wireless circuitry 24 may include transceivercircuitry 26 coupled to antenna 30 over signal path 28 (e.g., an opticalsignal path sometimes referred to herein as optical signal path 28). UTCPD 42 may be coupled between the radiating element arm(s) 36 of antenna30 and signal path 28. Transceiver circuitry 26 may include opticalcomponents 68, amplifier circuitry such as power amplifier 76, anddigital-to-analog converter (DAC) 74. Optical components 68 may includean optical receiver such as optical receiver 72 and optical localoscillator (LO) light sources (emitters) 70. LO light sources 70 mayinclude two or more light sources (e.g., sources of electromagneticenergy, light, or light energy) such as laser light sources, laserdiodes, optical phase locked loops, or other optical emitters that emitlight (e.g., electromagnetic energy, light, or light energy thatincludes optical local oscillator signals LO1 and LO2) at respectivewavelengths (e.g., visible, infrared, and/or ultraviolet wavelengths).If desired, LO light sources 70 may include a single light source andmay include optical components for splitting the light emitted by thelight source into different wavelengths. Signal path 28 may be coupledto optical components 68 over optical path 66. Optical path 66 mayinclude one or more optical fibers and/or waveguides.

Signal path 28 may include an optical splitter such as optical splitter(OS) 54, optical paths such as optical path 64 and optical path 62, anoptical combiner such as optical combiner (OC) 52, and optical path 40.Optical path 62 may be an optical fiber or waveguide. Optical path 64may be an optical fiber or waveguide. Optical splitter 54 may have afirst (e.g., input) port coupled to optical path 66, a second (e.g.,output) port coupled to optical path 62, and a third (e.g., output) portcoupled to optical path 64. Optical path 64 may couple optical splitter54 to a first (e.g., input) port of optical combiner 52. Optical path 62may couple optical splitter 54 to a second (e.g., input) port of opticalcombiner 52. Optical combiner 52 may have a third (e.g., output) portcoupled to optical path 40.

An optical phase shifter such as optical phase shifter 80 may be(optically) interposed on or along optical path 64. An optical modulatorsuch as optical modulator 56 may be (optically) interposed on or alongoptical path 62. Optical modulator 56 may be, for example, aMach-Zehnder modulator (MZM) and may therefore sometimes be referred toherein as MZM 56. MZM 56 includes a first optical arm (branch) 60 and asecond optical arm (branch) 58 interposed in parallel along optical path62. Propagating optical local oscillator signal LO2 along arms 60 and 58of MZM 56 may, in the presence of a voltage signal applied to one orboth arms, allow different optical phase shifts to be imparted on eacharm before recombining the signal at the output of the MZM (e.g., whereoptical phase modulations produced on the arms are converted tointensity modulations at the output of MZM 56). When the voltage appliedto MZM 56 includes wireless data, MZM 56 may modulate the wireless dataonto optical local oscillator signal LO2. If desired, the phase shiftingperformed at MZM 56 may be used to perform beam forming/steering inaddition to or instead of optical phase shifter 80. MZM 56 may receiveone or more bias voltages W_(BIAS) (sometimes referred to herein as biassignals W_(BIAS)) applied to one or both of arms 58 and 60. Controlcircuitry 14 (FIG. 1 ) may provide bias voltage W_(BIAS) with differentmagnitudes to place MZM 56 into different operating modes (e.g.,operating modes that suppress optical carrier signals, operating modesthat do not suppress optical carrier signals, etc.).

Intermediate frequency signal path 44 may couple UTC PD 42 to MZM 56(e.g., arm 60). An amplifier such as low noise amplifier 82 may beinterposed on intermediate frequency signal path 44. Intermediatefrequency signal path 44 may be used to pass intermediate frequencysignals SIGIF from UTC PD 42 to MZM 56. DAC 74 may have an input coupledto up-conversion circuitry, modulator circuitry, and/or basebandcircuitry in a transmitter of transceiver circuitry 26. DAC 74 mayreceive digital data to transmit over antenna 30 and may convert thedigital data to the analog domain (e.g., as data DAT). DAC 74 may havean output coupled to transmit data path 78. Transmit data path 78 maycouple DAC 74 to MZM 56 (e.g., arm 60). Each of the components alongsignal path 28 may allow the same antenna 30 to both transmit THFsignals 32 and receive THF signals 34 (e.g., using the same componentsalong signal path 28), thereby minimizing space and resource consumptionwithin device 10.

LO light sources 70 may produce (emit) optical local oscillator signalsLO1 and LO2 (e.g., at different wavelengths that are separated by thewavelength of THF signals 32/34). Optical components 68 may includelenses, waveguides, optical couplers, optical fibers, and/or otheroptical components that direct the emitted optical local oscillatorsignals LO1 and LO2 towards optical splitter 54 via optical path 66.Optical splitter 54 may split the optical signals on optical path 66(e.g., by wavelength) to output optical local oscillator signal LO1 ontooptical path 64 while outputting optical local oscillator signal LO2onto optical path 62.

Control circuitry 14 (FIG. 1 ) may provide phase control signals CTRL tooptical phase shifter 80. Phase control signals CTRL may control opticalphase shifter 80 to apply optical phase shift S to the optical localoscillator signal LO1 on optical path 64. Phase shift S may be selectedto steer a signal beam of THF signals 32/34 in a desired pointingdirection. Optical phase shifter 80 may pass the phase-shifted opticallocal oscillator signal LO1 (denoted as LO1+S) to optical combiner 52.Signal beam steering is performed in the optical domain (e.g., usingoptical phase shifter 80) rather than in the THF domain because thereare no satisfactory phase shifting circuit components that operate atfrequencies as high as the frequencies of THF signals 32 and 34. Opticalcombiner 52 may receive optical local oscillator signal LO2 over opticalpath 62. Optical combiner 52 may combine optical local oscillatorsignals LO1 and LO2 onto optical path 40, which directs the opticallocal oscillator signals onto UTC PD 42 for use during signaltransmission or reception.

During transmission of THF signals 32, DAC 74 may receive digitalwireless data (e.g., data packets, frames, symbols, etc.) fortransmission over THF signals 32. DAC 74 may convert the digitalwireless data to the analog domain and may output (transmit) the dataonto transmit data path 78 as data DAT (e.g., for transmission viaantenna 30). Power amplifier 76 may amplify data DAT. Transmit data path78 may pass data DAT to MZM 56 (e.g., arm 60). MZM 56 may modulate dataDAT onto optical local oscillator signal LO2 to produce modulatedoptical local oscillator signal LO2′ (e.g., an optical local oscillatorsignal at the frequency/wavelength of optical local oscillator signalLO2 but that is modulated to include the data identified by data DAT).Optical combiner 52 may combine optical local oscillator signal LO1 withmodulated optical local oscillator signal LO2′ at optical path 40.

Optical path 40 may illuminate UTC PD 42 with (using) optical localoscillator signal LO1 (e.g., with the phase shift S applied by opticalphase shifter 80) and modulated optical local oscillator signal LO2′.Control circuitry 14 (FIG. 1 ) may apply a control signal V_(BIAS) toUTC PD 42 that configures antenna 30 for the transmission of THF signals32. UTC PD 42 may convert optical local oscillator signal LO1 andmodulated optical local oscillator signal LO2′ into antenna currents onradiating element arm(s) 36 at the frequency of THF signals 32 (e.g.,while programmed for transmission using control signal V_(BIAS)). Theantenna currents on radiating element arm(s) 36 may radiate THF signals32. The frequency of THF signals 32 is given by the difference infrequency between optical local oscillator signal LO1 and modulatedoptical local oscillator signal LO2′. Control signals V_(BIAS) maycontrol UTC PD 42 to preserve the modulation from modulated opticallocal oscillator signal LO2′ in the radiated THF signals 32. Externalequipment that receives THF signals 32 will thereby be able to extractdata DAT from the THF signals 32 transmitted by antenna 30.

During reception of THF signals 34, MZM 56 does not modulate any dataonto optical local oscillator signal LO2. Optical path 40 thereforeilluminates UTC PD 42 with optical local oscillator signal LO1 (e.g.,with phase shift S) and optical local oscillator signal LO2. Controlcircuitry 14 (FIG. 1 ) may apply a control signal V_(BIAS) (e.g., a biasvoltage) to UTC PD 42 that configures antenna 30 for the receipt of THFsignals 32. UTC PD 42 may use optical local oscillator signals LO1 andLO2 to convert the received THF signals 34 into intermediate frequencysignals SIGIF output onto intermediate frequency signal path 44 (e.g.,while programmed for reception using bias voltage V_(BIAS)).Intermediate frequency signals SIGIF may include the modulated data fromthe received THF signals 34. Low noise amplifier 82 may amplifyintermediate frequency signals SIGIF, which are then provided to MZM 56(e.g., arm 60). MZM 56 may convert intermediate frequency signals SIGIFto the optical domain as optical signals LOrx (e.g., by modulating thedata in intermediate frequency signals SIGIF onto one of the opticallocal oscillator signals) and may pass the optical signals to opticalreceiver 72 in optical components 68, as shown by arrow 63 (e.g., viaoptical paths 62 and 66 or other optical paths). Control circuitry 14(FIG. 1 ) may use optical receiver 72 to convert optical signals LOrx toother formats and to recover (demodulate) the data carried by THFsignals 34 from the optical signals. In this way, the same antenna 30and signal path 28 may be used for both the transmission and receptionof THF signals while also performing beam steering operations.

The example of FIG. 6 in which intermediate frequency signals SIGIF areconverted to the optical domain is merely illustrative. If desired,transceiver circuitry 26 may receive and demodulate intermediatefrequency signals SIGIF without first passing the signals to the opticaldomain. For example, transceiver circuitry 26 may include ananalog-to-digital converter (ADC), intermediate frequency signal path 44may be coupled to an input of the ADC rather than to MZM 56, and the ADCmay convert intermediate frequency signals SIGIF to the digital domain.As another example, intermediate frequency signal path 44 may be omittedand control signals V_(BIAS) may control UTC PD 42 to directly sampleTHF signals 34 with optical local oscillator signals LO1 and LO2 to theoptical domain. As an example, UTC PD 42 may use the received THFsignals 34 and control signals V_(BIAS) to produce an optical signal onoptical path 40. The optical signal may have an optical carrier withsidebands that are separated from the optical carrier by a fixedfrequency offset (e.g., 30-100 GHz, 60 GHz, 50-70 GHz, 10-100 GHz,etc.). The sidebands may be used to carry the modulated data from thereceived THF signals 34. Signal path 28 may direct (propagate) theoptical signal produced by UTC PD 42 to optical receiver 72 in opticalcomponents 68 (e.g., via optical paths 40, 64, 62, 66, 63, and/or otheroptical paths). Control circuitry 14 (FIG. 1 ) may use optical receiver72 to convert the optical signal to other formats and to recover(demodulate) the data carried by THF signals 34 from the optical signal(e.g., from the sidebands of the optical signal).

If desired, optical components 68 may include clocking circuitry such asclocking (CLK) circuitry 75 (sometimes referred to herein as clockcircuitry 75 or clock generation circuitry 75). Clocking circuitry 75may include one or more electro-optical phase-locked loops (OPLLs),frequency locked loops (FLLs), and self-injection locked (locking)loops. As shown in FIG. 6 , clocking circuitry 75 may be used to controland clock LO light sources 70 and/or to clock any other desired hardwarein device 10 (e.g., clocking circuitry 75 need not be located intransceiver 26 and may, in general, be located elsewhere in device 10).LO light sources 70 may, for example, generate optical LO signals thatare phase-locked, self-injection locked, and optionally frequency-lockedwith respect to each other using clocking circuitry 75.

FIG. 7 is a circuit diagram showing one example of how multiple antennas30 may be integrated into a phased antenna array 88 that conveys THFsignals over a corresponding signal beam. In the example of FIG. 7 ,MZMs 56, intermediate frequency signal paths 44, data paths 78, andoptical receiver 72 of FIG. 6 have been omitted for the sake of clarity.Each of the antennas in phased antenna array 88 may alternatively samplereceived THF signals directly into the optical domain or may passintermediate frequency signals SIGIF to ADCs in transceiver circuitry26.

As shown in FIG. 7 , phased antenna array 88 includes N antennas 30 suchas a first antenna 30-0, a second antenna 30-1, and an Nth antenna30-(N−1). Each of the antennas 30 in phased antenna array 88 may becoupled to optical components 68 via a respective optical signal path(e.g., optical signal path 28 of FIG. 6 ). Each of the N signal pathsmay include a respective optical combiner 52 coupled to the UTC PD 42 ofthe corresponding antenna 30 (e.g., the UTC PD 42 in antenna 30-0 may becoupled to optical combiner 52-0, the UTC PD 42 in antenna 30-1 may becoupled to optical combiner 52-1, the UTC PD 42 in antenna 30-(N−1) maybe coupled to optical combiner 52-(N−1), etc.). Each of the N signalpaths may also include a respective optical path 62 and a respectiveoptical path 64 coupled to the corresponding optical combiner 52 (e.g.,optical paths 64-0 and 62-0 may be coupled to optical combiner 52-0,optical paths 64-1 and 62-1 may be coupled to optical combiner 52-1,optical paths 64-(N−1) and 62-(N−1) may be coupled to optical combiner52-(N−1), etc.).

Optical components 68 may include LO light sources 70 such as a first LOlight source 70A and a second LO light source 70B. The optical signalpaths for each of the antennas 30 in phased antenna array 88 may shareone or more optical splitters 54 such as a first optical splitter 54Aand a second optical splitter 54B. LO light source 70A may generate(e.g., produce, emit, transmit, etc.) first optical local oscillatorsignal LO1 and may provide first optical local oscillator signal LO1 tooptical splitter 54A via optical path 66A. Optical splitter 54A maydistribute first optical local oscillator signal LO1 to each of the UTCPDs 42 in phased antenna array 88 over optical paths 64 (e.g., opticalpaths 64-0, 64-1, 64-(N−1), etc.). Similarly, LO light source 70B maygenerate (e.g., produce, emit, transmit, etc.) second optical localoscillator signal LO2 and may provide second optical local oscillatorsignal LO2 to optical splitter 54B via optical path 66B. Opticalsplitter 54B may distribute second optical local oscillator signal LO2to each of the UTC PDs 42 in phased antenna array 88 over optical paths62 (e.g., optical paths 62-0, 62-1, 62-(N−1), etc.).

A respective optical phase shifter 80 may be interposed along (on) eachoptical path 64 (e.g., a first optical phase shifter 80-0 may beinterposed along optical path 64-0, a second optical phase shifter 80-1may be interposed along optical path 64-1, an Nth optical phase shifter80-(N−1) may be interposed along optical path 64-(N−1), etc.). Eachoptical phase shifter 80 may receive a control signal CTRL that controlsthe phase S provided to optical local oscillator signal LO1 by thatoptical phase shifter (e.g., first optical phase shifter 80-0 may impartan optical phase shift of zero degrees/radians to the optical localoscillator signal LO1 provided to antenna 30-0, second optical phaseshifter 80-1 may impart an optical phase shift of Δϕ to the opticallocal oscillator signal LO1 provided to antenna 30-1, Nth optical phaseshifter 80-(N−1) may impart an optical phase shift of (N−1)Δϕ to theoptical local oscillator signal LO1 provided to antenna 30-(N−1), etc.).By adjusting the phase S imparted by each of the N optical phaseshifters 80, control circuitry 14 (FIG. 1 ) may control each of theantennas 30 in phased antenna array 88 to transmit THF signals 32 and/orto receive THF signals 34 within a formed signal beam 83. Signal beam 83may be oriented in a particular beam pointing direction (angle) 84(e.g., the direction of peak gain of signal beam 83). The THF signalsconveyed by phased antenna array 88 may have wavefronts 86 that areorthogonal to beam pointing direction 84. Control circuitry 14 mayadjust beam pointing direction 84 over time to point towards externalcommunications equipment or an external object or to point away fromexternal objects, as examples.

Phased antenna array 88 may be operable in an active mode in which thearray transmits and/or receives THF signals using optical localoscillator signals LO1 and LO2 (e.g., using phase shifts provided toeach antenna element to steer signal beam 83). If desired, phasedantenna array 88 may also be operable in a passive mode in which thearray does not transmit or receive THF signals. Instead, in the passivemode, phased antenna array 88 may be configured to form a passivereflector that reflects THF signals or other electromagnetic wavesincident upon device 10. In the passive mode, the UTC PDs 42 in phasedantenna array 88 are not illuminated by optical local oscillator signalsLO1 and LO2 and transceiver circuitry 26 performs nomodulation/demodulation, mixing, filtering, detection, modulation,and/or amplifying of the incident THF signals.

Devices with processing capabilities include clocking circuitry such asphase-locked loops (PLLs) that generate clock signals. Devices with THFsignaling capabilities such as device 10 are particularly sensitive tojitter (deviations from perfect periodicity) and phase noise frequencygeneration in clock signals (e.g., because the clocking circuitryconsumes a relatively high amount of power and chip area for THFfrequencies). To minimize clock jitter and phase noise, processingoperations in device 10 may be clocked using clocking circuitry 75.Examples in which THF communications using transceiver 26 (FIG. 1 ) areclocked using clocking circuitry 75 are described herein as an example.This is merely illustrative and, in general, clocking circuitry 75 maybe used to clock any desired processing operations in device 10 (e.g.,high speed digital interface operations, processor computations,sensing, automotive, input/output operations, communications atfrequencies lower than 100 GHz such as millimeter/centimeter wavefrequencies or frequencies less than 10 GHz, etc.).

FIG. 8 is a circuit diagram of clocking circuitry 75. As shown in FIG. 8, clocking circuitry 75 may include an oscillator such as referenceoscillator 92, a phase detector (PD) such as phase detector 128, a loopfilter such as loop filter 125, a photodiode such photodiode 118, adivider such as divider 122, a first light source such as primary laser116 (e.g., from LO light sources 70 of FIG. 6 ), a second light sourcesuch as secondary laser 102 (e.g., from LO light sources 70 of FIG. 6 ),a first mixer such as mixer 140, a second mixer such as mixer 146, and adelay line such as delay line 152 (sometimes referred to herein as delaycircuitry 152 or optical delayer 152). If desired, clocking circuitry 75may optionally include frequency-locked loop (FLL) circuitry such as FLLcircuitry 98.

Photodiode 118 may be a UTC PD or another type of photodiode. Divider122 may be a divider circuit and/or may include sub-sampling circuitry(e.g., a sub-sampling mixer that sub-samples based on an oscillatorsignal from reference oscillator 92 or another reference oscillator).First mixer 140 may be an optical (e.g., electro-optical) mixer and mayinclude a photodiode such as a UTC PD, for example. First mixer 140 mayinclude a separate UTC PD from UTC PD 118 or, if desired, clockingcircuitry 75 may be adapted to use the same UTC PD to perform both thefunctions of first mixer 140 and UTC PD 118 as described herein (e.g.,optical splitters, combiners, couplers, paths, and/or switches may beused to route the optical local oscillator signals as described hereinto the shared UTC PD as needed based on whether the functions of UTC PD118 or the functions of first mixer 140 as described herein are beingperformed). Second mixer 146 may be an electro-optical mixer (e.g., anelectro-optical modulator) such as an MZM, for example.

Reference oscillator 92 may have an output coupled to a first input ofphase detector 128 over path 94. The output of reference oscillator 92may also be coupled to an input of FLL circuitry 98 over path 96 ifdesired. Phase detector 128 may have a second input coupled to theoutput of divider 122 over path 124. The output of phase detector 128may be coupled to a control input of secondary laser 102 over path 126.Path 126 may sometimes be referred to herein as a control path or aphase-locked loop (PLL) control path for secondary laser 102.

Loop filter 125 may be interposed on path 124 between phase detector 128and secondary laser 102. The input of divider 122 may be coupled to theoutput of UTC PD 118 over path 120. If desired, path 120 and the outputof UTC PD 118 may also be coupled to a control input of secondary laser102 over path 100. Path 100 may sometimes be referred to herein as acontrol path or a frequency-locked loop (FLL) control path for secondarylaser 102. FLL circuitry 98 may be interposed on path 100 between UTC PD118 and secondary laser 102. FLL circuitry 98 may include a counter,filter circuitry, or other circuitry involved in performing an FLLaround secondary laser 102.

Secondary laser 102 may have an output coupled to optical node 104.Optical node 104 may couple the output of secondary laser 102 to opticalnode 134 over optical path 106 and to output terminal 108 of clockingcircuitry 75. Optical node 134 may couple optical path 106 to a firstinput of UTC PD 118 over optical path 136 and to a first input of firstmixer 140 over optical path 138 (e.g., the first input of first mixer140 and the first input of UTC PD 118 may be optically coupled tosecondary laser 102). Optical node 104 and optical node 134 may eachinclude one or more optical splitters, optical combiners, opticalswitches, optical lenses, optical waveguides, optical fibers, opticalprisms, optical beam splitters, and/or optical couplers. If desired,optical nodes 104 and 134 may include one or more of the same (shared)optical splitters, optical combiners, optical switches, optical lenses,optical prisms, optical beam splitters, optical fibers, opticalwaveguides, and/or optical couplers (e.g., optical path 106 may beomitted and optical node 104 may also form optical node 134, such thatone or more of the same optical splitters, optical combiners, opticalfibers, optical waveguides, optical switches, optical lenses, opticalprisms, optical beam splitters, and/or optical couplers couples theoutput of secondary laser 102 to output terminal 108, the first input ofUTC PD 118, and the first input of first mixer 140).

Primary laser 116 may have an output coupled to optical node 112.Optical node 112 may couple the output of primary laser 116 to outputterminal 110 of clocking circuitry 75, a second input of UTC PD 118 overoptical path 114, and optical node 142 over optical path 144 (e.g., thesecond input of UTC PD 118 may be optically coupled to primary laser116). Optical node 142 may couple optical path 144 to a second input offirst mixer 140 and to a first input of second mixer 146 (e.g., thesecond input of first mixer 140 may be optically coupled to primarylaser 116 and the first input of second mixer 146 may be opticallycoupled to primary laser 116). Optical node 112 and optical node 142 mayeach include one or more optical splitters, optical combiners, opticalswitches, optical fibers, optical waveguides, optical lenses, opticalprisms, optical beam splitters, and/or optical couplers. If desired,optical nodes 112 and 142 may include one or more of the same (shared)optical splitters, optical combiners, optical switches, optical lenses,optical prisms, optical fibers, optical waveguides, optical beamsplitters, and/or optical couplers (e.g., optical path 144 may beomitted and optical node 112 may also form optical node 142, such thatone or more of the same optical splitters, optical combiners, opticalswitches, optical lenses, optical prisms, optical fibers, opticalwaveguides, optical beam splitters, and/or optical couplers couples theoutput of primary laser 116 to output terminal 110, the second input ofUTC PD 118, the second input of first mixer 140, and the first input ofsecond mixer 146).

First mixer 140 may have an output (communicably) coupled to a secondinput of second mixer 146 over path 148. Second mixer 146 may have anoutput coupled to an input of delay line 152 over optical path 150.Optical path 150 may sometimes be referred to herein as a control pathor a self-injection locking control path. Delay line 152 may have anoutput coupled to a control input of secondary laser 102 (e.g., theoutput of second mixer 146 may be optically or communicably coupled tothe control input secondary laser 102 via optical path 150 and delayline 152). Delay line 152 may include one or more optical delay elementsconfigured to introduce a delay to the signals on optical path 150.Delay line 152 may also generate an error signal if desired. The opticalpaths in clocking circuitry 75 (e.g., optical paths 106, 138, 136, 114,144, 148, and 150) may include optical fibers and/or optical waveguides.Paths 120, 100, 124, 98, 124, 96, and 148 may include conductive paths(e.g., radio-frequency transmission line structures or other paths) thatconvey current rather than optical signals.

Output terminals 108 and 110 may provide optical LO signals that areused to clock other components in device 10. In implementations whereclocking circuitry 75 is used to clock THF communications usingtransceiver 26 (FIG. 1 ), terminal 108 may be coupled to optical path 62and terminal 110 may be coupled to optical path 64 of FIG. 6 , forexample. Clocking circuitry 75 may include multiple control/feedbackloops that are used to minimize phase noise and jitter in the optical LOsignals provided to output terminals 108 and 110. As shown in FIG. 8 ,clocking circuitry 75 may include at least a PLL (e.g., an OPLL) aroundsecondary laser 102 and a self-injection locking loop around secondarylaser 102.

For example, UTC PD 118, path 120, divider 122, path 124, phase detector128, path 126, loop filter 125, secondary laser 102, optical path 106,and optical path 136 may form a PLL as shown by PLL path 130. On theother hand, secondary laser 102, optical path 106, optical path 138,first mixer 140, path 148, second mixer 146, optical path 150, and delayline 152 may form a self-injection locking loop as shown byself-injection locking loop path 154. Primary laser 116, secondary laser102, first mixer 140, second mixer 146, path 148, optical path 150,delay line 152, optical node 104, optical node 134, optical node 112,optical node 142, and optical paths 144, 138, and 106 may collectivelyform self-injection locking loop circuitry 90. If desired, clockingcircuitry 75 may also include an optional frequency-locked loop (FLL)around secondary laser 102 and the PLL (e.g., the PLL may be nestedwithin the FLL). For example, UTC PD 118, path 120, path 100, FLLcircuitry 98, secondary laser 102, optical path 106, and optical path136 may form an FLL as shown by FLL path 132.

Primary laser 116 may generate optical local oscillator signal LO1 onoutput terminal 110. Secondary laser 102 may generate optical localoscillator signal LO2 on output terminal 108. During generation ofoptical LO signals LO1 and LO2, clocking circuitry 75 may use the PLL,the self-injection locking loop (sometimes referred to herein as aself-injection locked loop), and optionally the FLL to actively adjustsecondary laser 102 to minimize phase noise and jitter. For example, FLLpath 132, PLL path 130, and self-injection locking loop path 154 mayeach be feedback paths for secondary laser 102 (e.g., feedback pathsthat communicably couple the output of secondary laser 102 to the(control) input(s) of secondary laser 102. The FLL may be used tocoarsely adjust (tune) secondary laser 102 until secondary laser 102 isfrequency locked with primary laser 116 (e.g., until optical localoscillator signal LO1 is frequency locked with optical local oscillatorsignal LO2 such that there is a selected/predetermined stable frequencydifference between the two optical local oscillators). The PLL may beused to less-coarsely adjust (tune) secondary laser 102 until secondarylaser 102 is phase locked with primary laser 116 (e.g., until opticallocal oscillator signal LO1 is phase locked with optical localoscillator signal LO2). The self-injection locking loop may be used tofine tune secondary laser 102 to further reduce the phase noise andjitter of secondary laser 102, thereby optimizing the processingoperations performed by device 10 using optical local oscillator signalsLO1 and LO2.

While described herein as lasers, primary laser 116 and secondary laser102 may be any desired light sources/emitters. Lasers 116 and 102 mayform LO light sources 70 of FIG. 7 and/or may respectively form LO lightsources 70A and 70B of FIG. 7 , for example. Primary laser 116 maysometimes also be referred to as a leader laser whereas secondary laser102 is sometimes also referred to as a follower laser. Primary laser 116may emit optical local oscillator signal LO1′ at a fixedfrequency/wavelength (e.g., primary laser 116 may be a fixed(non-adjustable) laser having a fixed frequency). On the other hand,secondary laser 102 may emit optical local oscillator signal LO2′ at anadjustable/programmable frequency/wavelength (e.g., secondary laser 102may be an adjustable/programmable laser). Control signals received bysecondary laser 102 over paths 126, 100, and 150 may be used toadjust/program the frequency and/or phase of optical local oscillatorsignal LO2′. The wavelength of optical local oscillator signal LO2′ maybe offset from the wavelength of optical local oscillator signal LO1′ bya selected wavelength offset X (e.g., the frequencies of the THF signalsto be transmitted and/or received using optical local oscillator signalsLO1 and LO2).

Optical node 104 may transmit a first amount of power from optical localoscillator signal LO2′ to UTC PD 118 and/or first mixer 140 as opticallocal oscillator signal LO2″. Optical node 104 may transmit a secondamount of power from optical local oscillator signal LO2′ to outputterminal 108 as optical local oscillator signal LO2 (e.g., where thesecond amount of power is greater than the first amount). As an example,optical node 104 may provide 10% of the power of optical localoscillator signal LO2′ to UTC PD 118 or first mixer 140 as optical localoscillator signal LO2″ and may provide 90% of the power of optical localoscillator signal LO2′ to output terminal 108 as optical localoscillator signal LO2.

At the same time, optical node 112 may transmit a first amount of powerfrom optical local oscillator signal LO1′ to UTC PD 118 over opticalpath 114 and/or to mixers 140 and 146 as optical local oscillator signalLO1″. Optical node 112 may transmit a second amount of power fromoptical local oscillator signal LO1′ to output terminal 110 as opticallocal oscillator signal LO1 (e.g., where the second amount of power isgreater than the first amount). As an example, optical node 112 mayprovide 10% of the power of optical local oscillator signal LO1′ to UTCPD 118 or to mixers 140 and 146 as optical local oscillator signal LO1″and may provide 90% of the power of optical local oscillator signal LO1′to output terminal 110 as optical local oscillator signal LO1. Opticallocal oscillator signals LO2″ and LO1″ may be processed by the FLL, thePLL, and the self-injection locking loop in clocking circuitry 75 tofrequency lock and phase lock optical local oscillator signals LO1 andLO2 while minimizing the phase noise and jitter of optical localoscillator signal LO2.

During tuning of secondary laser 102 using FLL path 132 and PLL path130, UTC PD 118 may generate and output photodiode signal PD_SIG on path120 based on the optical local oscillator signals LO2″ and LO1″ receivedover optical paths 136 and 114. Photodiode signal PD_SIG may be at afrequency given by the difference between the frequency of optical localoscillator signal LO2″ and the frequency of optical local oscillatorsignal LO1″ (e.g., the frequency of THF signals 32/34 of FIG. 6 ). Path120 may convey photodiode signal PD_SIG to divider 122 when the PLLtunes secondary laser 102 and may convey photodiode signal PD_SIG to FLLcircuitry 98 via path 100 when the FLL tunes secondary laser 102.

During tuning of secondary laser 102 using FLL path 132 and PLL path130, reference oscillator 92 may generate reference oscillator signalOSC. Reference oscillator 92 may, for example, be amicroelectromechanical systems (MEMS) oscillator, a crystal oscillator,or any other fixed or slightly tunable stable oscillator. Referenceoscillator signal OSC may be produced at a fixed radio frequency such asa frequency between around 5-25 GHz. Reference oscillator 92 may providereference oscillator signal OSC to phase detector 128 over path 94 andto FLL circuitry 98 over path 96 (e.g., to a counter in FLL circuitry98). If desired, reference oscillator 92 may include a digital-to-timeconverter (DTC) that generates a modified reference oscillator signalbased on reference oscillator signal OSC and may provide the modifiedreference oscillator signal to phase detector 128 and/or to divider 122(e.g., a sub-sampling mixer) during tuning of secondary laser 102 by thePLL. Phase detector 128 may produce an output signal PLL_CTRL (e.g., atuning control signal) that is provided to the control input ofsecondary laser 102 via loop filter 125. During tuning of secondarylaser 102 by the FLL, FLL circuitry 98 may produce an output signalFLL_CTRL (e.g., a tuning control signal) that is provided to the controlinput of secondary laser 102.

During reduction of the phase noise of secondary laser 102 usingself-injection locking loop circuitry 90, optical local oscillatorsignal LO2″ may be provided to the first input of first mixer 140 andoptical local oscillator signal LO1″ may be provided to the second inputof first mixer 140 and to the first input of second mixer 146. Firstmixer 140 may output beat signal BTS on path 148. Second mixer 146 mayproduce self-injection locking signal SILS on optical path 150 based onoptical local oscillator signal LO1″ and beat signal BTS (e.g., bymodulating optical local oscillator signal LO1″ with beat signal BTS).Delay line 152 may use self-injection locking signal SILS toself-injection lock secondary laser 102. Delay line 152 may include longspools of optical fibers and/or other optical delay components. Delayline 152 may introduce delay to the photons of self-injection lockingsignal SILS that serves to filter out phase noise from self-injectionlocking signal SILS.

The example of FIG. 8 is merely illustrative. Path 100 and FLL circuitry98 may be omitted. UTC PD 118 and/or first mixer 140 need not includeUTC PD(s) and may, in general, be an adjustable/programmable photodiodeor component that converts electromagnetic energy (e.g., light or lightenergy) at optical frequencies (e.g., ultraviolet frequencies, visiblefrequencies, and/or infrared frequencies) to current at THF frequencies(e.g., the same type of component used to produce current on antennaradiating element arms 36 using optical local oscillator signals LO1 andLO2 of FIG. 6 ). If desired, delay line 152 may be interposed on path148 instead of on optical path 150 between second mixer 146 andsecondary laser 102. FIG. 9 is a diagram of self-injection locking loopcircuitry 90 in an example where delay line 152 may be interposed onpath 148. The PLL and FLL of clocking circuitry 75 are not shown in FIG.9 for the sake of simplicity.

As shown in FIG. 9 , delay line 152 may be interposed on path 148between the output of first mixer 140 and the second input of mixer 146(e.g., the output of first mixer 140 may be communicably coupled to thesecond input of second mixer 146 via delay line 152). Optical path 150may be coupled to the control input of secondary laser 102 without adelay line. First mixer 140 may output beat signals BTS on path 148.Delay line 152 may delay beat signals BTS (e.g., in the electricaldomain) to de-correlate optical phase noise from the output of secondarylaser 102, which may allow phase noise reduction by self-injection atsecondary laser 102.

In other implementations, delay line 152 may be replaced with an opticalresonator interposed on optical path 150. FIG. 10 is a diagram ofself-injection locking loop circuitry 90 in an example where delay line152 of FIG. 8 has been replaced with an optical resonator. The PLL andFLL of clocking circuitry 75 are not shown in FIG. 10 for the sake ofsimplicity. As shown in FIG. 10 , an optical resonator such as resonator160 may be interposed on optical path 150 between the output of secondmixer 146 and the control input of secondary laser 102. Resonator 160may be a high-Q optical resonator. Resonator 160 may have an opticalresonance that causes photons from self-injection locking signal SILS toremain in resonance inside the resonator. The longer the photons remaincirculating within the resonator, the more phase noise can be eliminatedfrom self-injection locking signal SILS. The example of FIG. 10 ismerely illustrative and, if desired, resonator 160 may be coupledbetween first mixer 140 and second mixer 146 (e.g., delay line 152 ofFIG. 9 may be replaced with resonator 160).

The examples of FIG. 8-10 are merely illustrative. If desired, secondarylaser 102 and primary laser 116 may share the same resonating cavity(e.g., secondary laser 102 may utilize a longer or shorter portion ofthe resonating cavity than primary laser 116 to allow for the differencein wavelength between the optical local oscillator signals). Sharing acommon resonating cavity between secondary laser 102 and primary laser116 may cause secondary laser 102 and primary laser 116 to exhibit verysimilar thermal effects, thereby helping to tightly lock secondary laser102 to primary laser 116. The components of clocking circuitry 75 may beimplemented in hardware (e.g., one or more digital logic gates, digitalcircuits, analog circuits, one or more processors, etc.) and/or software(e.g., using logical/computational operations executed by one or moreprocessors).

FIG. 11 is a flow chart of illustrative operations involved in usingclocking circuitry 75 to generate optical local oscillator signals LO1and LO2 (e.g., to clock one or more components in device 10 such aswireless circuitry 24 of FIG. 1 ).

At optional operation 170, clocking circuitry 75 may coarsely tunesecondary laser 102 using FLL path 132 (FIG. 8 ). For example, primarylaser 116 and secondary laser 102 may begin to illuminate UTC PD 118using optical local oscillator signals LO2″ and LO1″. UTC PD 118 maygenerate photodiode signal PD_SIG based on optical local oscillatorsignals LO2″ and LO1″. Path 100 may convey photodiode signal PD_SIG toFLL circuitry 98. Reference oscillator 92 may begin to generatereference oscillator signal OSC and may provide reference oscillatorsignal OSC (or a modified reference oscillator signal) to FLL circuitry98 (e.g., to a counter in FLL circuitry 98). FLL circuitry 98 (e.g., thecounter) may identify the frequency of photodiode signal PD_SIG usingreference oscillator signal OSC as a reference.

Logic in FLL circuitry 98 (e.g., a comparator and/or other digitallogic) may compare the identified frequency to thepredetermined/expected/selected frequency of secondary laser 102. If theidentified frequency is excessively far from the expected frequency(e.g., if the difference between the identified frequency and theexpected frequency exceeds a threshold), FLL circuitry 98 may use outputsignal FLL_CTRL to coarsely adjust the frequency of secondary laser 102until the identified frequency is sufficiently close to the expectedfrequency. Output signal FLL_CTRL may coarsely tune the frequency ofsecondary laser 102 using input current adjustments, piezoelectricadjustments, mirror shifts, etc. When the identified frequency issufficiently close to the expected frequency (e.g., when the differencebetween the identified frequency and the expected frequency is less thanthe threshold), clocking circuitry 75 may lock the coarse tuning ofsecondary laser 102 (e.g., may frequency lock secondary laser 102 andoptical local oscillator signal LO2′). Processing may subsequentlyproceed to operation 160 via path 172. If desired, operation 170 may beomitted.

At operation 172, clocking circuitry 75 may less-coarsely tune secondarylaser 102 using PLL path 130 (FIG. 8 ) until the phase of photodiodesignal SIG_PD is sufficiently close to a predetermined or expectedphase. When the phase is sufficiently close to the expected phase,clocking circuitry 75 may lock the less-coarse tuning of secondary laser102 (e.g., may phase lock secondary laser 102 and optical localoscillator signal LO2′ to the phase of optical local oscillator signalLO1′).

At operation 174, clocking circuitry 75 may further reduce the phasenoise of secondary laser 102 (e.g., sometimes referred to herein asfine-tuning secondary laser 102) using self-injection locking loopcircuitry 90 (FIG. 8 ). This may involve the self-injection or feedbackof self-injection locking signal SILS into/onto secondary laser 102. Inother words, clocking circuitry 75 may use self-injection locking looppath 154 to self-injection lock secondary laser 102, thereby reducingphase noise.

At operation 176, clocking circuitry 75 may clock one or more processingoperations in device 10 using optical local oscillator signals LO1 andLO2 (e.g., device 10 may perform subsequent processing operations asclocked by optical local oscillator signals LO1 and LO2). For example,the UTC PDs 42 in device 10 may transmit and/or receive THF signalsusing the optical local oscillator signals LO1 and LO2 produced byclocking circuitry 75 with minimal phase noise and jitter.

FIG. 12 is a flow chart of illustrative operations that may be performedby clocking circuitry 75 to tune secondary laser 102 using PLL path 130of FIG. 8 . The operations of FIG. 12 may, for example, be performedwhile processing operation 172 of FIG. 11 .

At operation 180, primary laser 116 and secondary laser 102 may begin toilluminate UTC PD 118 using optical local oscillator signals LO2″ andLO1″.

At operation 182, UTC PD 118 may generate photodiode signal PD_SIG basedon optical local oscillator signals LO2″ and LO1″. The frequency ofphotodiode signal PD_SIG may be given by the difference between thefrequencies of optical local oscillator signals LO2″ and LO1″ (e.g., afrequency corresponding to wavelength offset X). Path 120 may conveyphotodiode signal PD_SIG to divider 122.

At operation 184, divider 122 may divide or subsample photodiode signalPD_SIG to a frequency close to a reference frequency. The referencefrequency may be the frequency of reference oscillator signal OSC, forexample. If desired, divider 122 may be a subsampling mixer thatprocesses photodiode signal PD_SIG based on a modified referenceoscillator signal produced by a DTC in reference oscillator 92. Divider122 may provide the divided (e.g., sub-sampled) photodiode signal PD_SIGto phase detector 128 over path 124.

At operation 186, phase detector 128 may compare the phase of thedivided photodiode signal PD_SIG on path 124 to the phase of referenceoscillator signal OSC (or the phase of the modified reference oscillatorsignal produced by a DTC in reference oscillator 92). Phase detector 128may include digital XOR logic and/or a phase detector and comparatorsometimes referred to herein collectively as a phase comparator. Inpractice, photodiode signal PD_SIG may be at much higher frequencies(e.g., 50-400 GHz) than reference oscillator signal OSC (e.g., 5-25GHz), making phase comparison difficult or impossible. As such,sub-sampling the photodiode signal using divider 122 may more easilyallow such a phase comparison (e.g., where the phase of the subsampledphotodiode signal is similar to the phase of the original photodiodesignal). Divider 122 may subsample photodiode signal PD_SIG by onlycomparing a regularly spaced subset of the samples in photodiode signalPD_SIG to reference oscillator signal OSC, for example (e.g., everyeighth sample of photodiode signal PD_SIG).

Phase detector 128 may include comparison logic that compares thedifference between the measured phase of photodiode signal PD_SIG (e.g.,the subsampled photodiode signal) and generates a corresponding errorsignal such as output signal PLL_CTRL. Output signal PLL_CTRL may be,for example, an error signal indicative of the phase error in theoptical local oscillator produced by secondary laser 102. At operation188, loop filter 125 may filter the error signal (e.g., using a 1-3 MHzfilter).

Comparison logic on PLL path 130 (e.g., in phase detector 128, loopfilter 125, etc.) may compare the difference between the phase of thedivided photodiode signal PD_SIG and the phase of reference oscillatorsignal OSC to a predetermined threshold value. If the phase ofphotodiode signal PD_SIG is excessively far from the phase of referenceoscillator signal OSC (e.g., if the difference exceeds a threshold),processing may proceed to operation 192 via path 190. At operation 192,PLL path 130 may use output signal PLL_CTRL to less-coarsely adjustsecondary laser 102 to begin outputting optical local oscillator signalsLO2′ at a different phase. Output signal PLL_CTRL may less-coarsely tunethe phase of secondary laser 102 by adjusting the input current of aphase shift section in secondary laser 102, for example.

Processing may loop back to operation 182 via path 194 and phasedetector 128 may continue re-measuring photodiode signal PD_SIG andfinely adjusting secondary laser 102 until the phase of photodiodesignal PD_SIG (e.g., the subsampled photodiode signal) is sufficientlyclose to the phase of reference oscillator signal OSC (e.g., until thedifference is less than a threshold), at which point processing mayproceed to operation 198 via path 196. At operation 198, clockingcircuitry 75 may lock (freeze) the phase of secondary laser 102 in place(e.g., may lock the less-coarse tuning of secondary laser). The opticallocal oscillator signals LO1 and LO2 subsequently generated by primarylaser 116 and secondary laser 102 may thereafter be frequency locked andphase locked. To further reduce phase noise, self-injection locking loopcircuitry 90 may then perform self-injection locking on secondary laser102.

FIG. 13 is a flow chart of illustrative operations that may be performedby clocking circuitry 75 to fine tune secondary laser 102 usingself-injection locking loop path 154 of FIG. 8 . The operations of FIG.13 may, for example, be performed while processing operation 174 of FIG.11 .

At operation 200, clocking circuitry 75 may begin to illuminate thefirst input of first mixer 140 with optical local oscillator signal LO2″and may begin to illuminate the second input of first mixer 140 and thefirst input of second mixer 146 with optical local oscillator signalLO1″.

At operation 202, first mixer 140 (e.g., a UTC PD or other photodiode)may generate beat signal BTS using (based on) first optical localoscillator signal LO1″ and second optical local oscillator signal LO2″.Beat signal BTS may have a frequency given by the difference between thefrequency of optical local oscillator signal LO1″ and the frequency ofoptical local oscillator signal LO2″ (e.g., a frequency corresponding towavelength offset X such as the frequency of THF signals 32/34).

At operation 204, second mixer 146 (e.g., an MZM or anotherelectro-optical mixer or modulator) may generate self-injection lockingsignal SILS on optical path 150 using (based on) first optical localoscillator signal LO1″ and beat signal BTS (e.g., by mixing ormodulating beat signal BTS onto first optical local oscillator signalLO1″). Modulation by second mixer 146 may generate two sideband signalsof a carrier formed by first optical local oscillator signal LO1″. Ifdesired, second mixer 146 may filter out one of the sideband signals,leaving self-injection locking signal SILS at a frequency equal to thefrequency of the optical local oscillator signal produced by secondlaser 102 (e.g., optical local oscillator signal LO2″).

At operation 206, delay line 152 may self-inject secondary laser 102using self-injection locking signal SILS. Delay line 152 may, forexample, optically delay self-injection locking signal SILS tode-correlate the phase noise of secondary laser 102 and then injectself-injection locking signal SILS into secondary laser 102, whichallows secondary laser 102 to reduce its phase noise via self-injectionlocking. Secondary laser 102 may, for example, include a laser cavitybetween two mirrors that keep photons within the laser cavity. Whenself-injection is performed, the self-injection locking signal SILS(e.g., an optical signal at the same frequency as optical localoscillator signal LO2′) is transmitted into the laser cavity from path150 through the mirror. The self-injected photons from self-injectionlocking signal SILS have been cleaned (de-correlated) of phase noise bydelay line 152 and may help secondary laser 102 to output optical localoscillator signal LO2′ (and thus the corresponding optical localoscillator signals LO2″ and LO2) with reduced phase noise. Iteratingover this process one or more times fine-tunes and self-injection lockssecondary laser 102. Self-injection locking signal SILS may sometimes bereferred to herein as a self-injection locking input signal after beingdelayed by delay line 152.

This example is merely illustrative. In implementations where delay line152 is replaced with a resonator such as resonator 160 in FIG. 10 ,resonator 160 may filter phase noise of self-injection locking signalSILS prior to feeding back to secondary laser 102. For example,resonator 160 may allow the photons in self-injection locking signalSILS to resonate and remain within resonator 160. The longer the photonsresonate and remain within resonator 160, the more phase noise iscleaned from the photons. Resonator 160 may allow phase noise cleaningwithout requiring long spools of optical fiber or other bulky componentsused to form delay line 152. In implementations where delay line 152 isdisposed on path 148 of FIG. 8 (e.g., as shown in FIG. 9 ), delay line152 may clean the phase noise from beat signal BTS rather thanself-injection locking signal SILS. If there is still excessive phasenoise in secondary laser 102, processing may proceed to operation 210via path 208, the fine tuning of secondary laser 102 may be adjusted(e.g., by continuing to iteratively self-inject secondary laser 102 bylooping processing back to operation 202 until phase noise has beensufficiently reduced). Once phase noise has been sufficiently reducedfor secondary laser 102, processing may proceed to operation 216 viapath 216 and clocking circuitry 75 may lock the fine tuning of secondarylaser 102.

Clocking circuitry 75 may then generate optical local oscillator signalsLO1 and LO2 for clocking other components in device 10 (e.g., to controlUTC PDs 42 in wireless circuitry 24 of FIGS. 6 and 7 to transmit and/orreceive THF signals) with minimal jitter and minimal phase noise.Generating optical local oscillator signals LO1 and LO2 in this way mayallow frequency tuning of 0.2% of one laser working for example, at afrequency of 200,300 GHz, which may be sufficient to cover any wantedfrequency for THF signals 32/34 from about 50 GHz to about 400 GHz. Atthe same time, the power efficiency of the laser light sources inclocking circuitry 75 may be greater than 30%, which is higher than inmillimeter wave communications and in voltage controlled oscillators(VCOs) that operate at sub-THz frequencies, which typically have a powerefficiency on the order of a few percent. Furthermore, to preventcross-talk between the generated sub-THz signal and the antennas andpower amplifiers operating at sub-THz frequencies, clocking circuitry 74may clock wireless circuitry 24 without requiring lossy inductive coils.

Device 10 may gather and/or use personally identifiable information. Itis well understood that the use of personally identifiable informationshould follow privacy policies and practices that are generallyrecognized as meeting or exceeding industry or governmental requirementsfor maintaining the privacy of users. In particular, personallyidentifiable information data should be managed and handled so as tominimize risks of unintentional or unauthorized access or use, and thenature of authorized use should be clearly indicated to users. Theoptical components described herein (e.g., MZM modulator(s),waveguide(s), phase shifter(s), UTC PD(s), etc.) may be implemented inplasmonics technology if desired.

The methods and operations described above in connection with FIGS. 1-13(e.g., the operations of FIGS. 11-13 ) may be performed by thecomponents of device 10 using software, firmware, and/or hardware (e.g.,dedicated circuitry or hardware). Software code for performing theseoperations may be stored on non-transitory computer readable storagemedia (e.g., tangible computer readable storage media) stored on one ormore of the components of device 10 (e.g., storage circuitry 16 of FIG.1 ). The software code may sometimes be referred to as software, data,instructions, program instructions, or code. The non-transitory computerreadable storage media may include drives, non-volatile memory such asnon-volatile random-access memory (NVRAM), removable flash drives orother removable media, other types of random-access memory, etc.Software stored on the non-transitory computer readable storage mediamay be executed by processing circuitry on one or more of the componentsof device 10 (e.g., processing circuitry 18 of FIG. 1 , etc.). Theprocessing circuitry may include microprocessors, central processingunits (CPUs), application-specific integrated circuits with processingcircuitry, or other processing circuitry.

The foregoing is merely illustrative and various modifications can bemade to the described embodiments. The foregoing embodiments may beimplemented individually or in any combination.

What is claimed is:
 1. Clocking circuitry comprising: a first lightsource configured to generate a first optical LO signal at a firstfrequency; a second light source configured to generate a second opticalLO signal at a second frequency different from the first frequency; afirst mixer having a first input optically coupled to the first lightsource and having a second input optically coupled to the second lightsource; and a second mixer having a first input optically coupled to thefirst light source, a second input communicably coupled to an output ofthe first mixer, and an output optically coupled to the second lightsource.
 2. The clocking circuitry of claim 1, wherein the first mixer isconfigured to generate a beat signal based on the first optical LOsignal and the second optical LO signal.
 3. The clocking circuitry ofclaim 2, wherein the second mixer is configured to generate aself-injection locking signal based on the beat signal and the firstoptical LO signal.
 4. The clocking circuitry of claim 3, furthercomprising: a delay line having an input coupled to the output of thesecond mixer and having an output coupled to the second light source,wherein the delay line is configured to self-inject the self-injectionlocking signal onto the second light source.
 5. The clocking circuitryof claim 1, further comprising: an optical path that couples the outputof the second mixer to the second light source; and an optical resonatordisposed on the optical path, wherein the optical resonator isconfigured to self-inject the self-injection locking signal onto thesecond light source.
 6. The clocking circuitry of claim 1, furthercomprising: a path that couples the output of the first mixer to thesecond input of the second light source; and a delay line disposed onthe path.
 7. The clocking circuitry of claim 1, wherein the first lightsource comprises a first laser and the second light source comprises asecond laser.
 8. The clocking circuitry of claim 1, wherein the firstmixer comprises a photodiode and the second mixer comprises anelectro-optical modulator.
 9. The clocking circuitry of claim 1, whereinthe second mixer comprises a Mach-Zehnder modulator (MZM).
 10. Theclocking circuitry of claim 1, wherein the first mixer comprises auni-travelling-carrier photodiode (UTC PD).
 11. The clocking circuitryof claim 1, further comprising: a photodiode having a first inputoptically coupled to the first light source and a second input opticallycoupled to the second light source.
 12. The clocking circuitry of claim10, further comprising a phase-locked loop (PLL) path that includes: thephotodiode; a divider coupled to an output of the photodiode; a phasedetector having a first input coupled to an output of the divider and asecond input that receives a reference oscillator signal; and a loopfilter coupled between an output of the phase detector and the secondlight source.
 13. Clocking circuitry comprising: a first laserconfigured to generate a first optical local oscillator (LO) signal; asecond laser configured to generate a second optical LO signal; aphase-locked loop (PLL) path coupled around the second laser andconfigured to lock a phase of the second optical LO signal to a phase ofthe first optical LO signal; and a self-injection locking loop pathcoupled around the second laser and configured to self-injection lockthe second laser.
 14. The clocking circuitry of claim 13, wherein theself-injection locking loop path comprises: a delay line or an opticalresonator configured to self-inject a signal from the self-injectionlocking loop path onto the second laser.
 15. The clocking circuitry ofclaim 14, wherein the self-injection locking loop path comprises: aphotodiode configured to mix the first optical LO signal with the secondoptical LO signal to generate a beat signal; and an electro-opticalmodulator configured to generate the signal on the self-injectionlocking loop path by modulating the first optical LO signal with thebeat signal.
 16. The clocking circuitry of claim 13 wherein the PLL looppath comprises: a uni-travelling-carrier photodiode (UTC PD) having afirst input that receives the first optical LO signal and a second inputthat receives the second optical LO signal; a sub-sampling mixer havingan input coupled to an output of the UTC PD; a phase detector having aninput coupled to an output of the sub-sampling mixer; and a loop filtercoupled between an output of the phase detector and the second laser.17. The clocking circuitry of claim 13, further comprising: afrequency-locked loop (FLL) path coupled around the PLL path andconfigured to lock a frequency of the second optical LO signal to afrequency of the first optical LO signal.
 18. A method of operatingwireless circuitry to transmit wireless signals, the method comprising:emitting, at a first laser, a first optical local oscillator (LO) signalat a first frequency; emitting, at a second laser, a second optical LOsignal at a second frequency that is different from the first frequency;producing, at a first photodiode illuminated by the first optical LOsignal and the second optical LO signal, an antenna current on anantenna resonating element, the antenna current having a third frequencygiven by a difference between the first frequency and the secondfrequency; generating, at a second photodiode, a beat signal based onthe first optical LO signal and the second optical LO signal, the beatsignal having the third frequency; generating, at a mixer, aself-injection locking signal based on the beat signal and the firstoptical LO signal; and self-injection locking the second laser based onthe self-injection locking signal.
 19. The method of claim 18, furthercomprising: phase locking, using a phase-locked loop (PLL) path, thefirst optical LO signal to the second optical LO signal.
 20. The methodof claim 19, wherein phase locking the first optical LO signal to thesecond optical LO signal comprises: generating, at a third photodiode, aphotodiode signal based on the first optical LO signal and the secondoptical LO signal, the photodiode signal having the third frequency;generating, at a phase detector, an error signal based on the photodiodesignal and a reference oscillator signal; and tuning the second laserbased on the error signal.